The present invention relates to a getter device for active systems for the transdermal release of drugs.
Systems for the transdermal release of drugs are used in the treatment of conditions, dysfunctions or diseases requiring a regular administration of drugs to a patient, such as post-operative aches, cardiovascular diseases or diabetes. These systems essentially consist of an envelope of polymeric material having on the inside the drug to be dispensed, generally in form of suspension in a gel. A portion of the envelope surface is made of a plastic material permeable to the drug. By causing this portion of the envelope to adhere to the patient's skin (e.g., on an arm), the drug is released onto and absorbed by the skin itself, then entering the blood stream.
The first transdermal systems, appeared at the beginning of 1990s, were of the so-called passive type, wherein the drug release was determined only by the velocity of absorption by the skin. These systems have a number of drawbacks, such as the fact that it is impossible to control the drug flow (and consequently its dosing over a unit of time), as well as that it is impossible to have intermittent administrations, only for prefixed durations of time and at prefixed intervals or only upon the patient's request, which on the contrary are the more appropriate administration modes in some cases.
Therefore, more recently, active systems for releasing drugs have been introduced which are based on ionophoresis, i.e., transportation of drugs in ionic form under the effect of electrical fields. An example of this kind of apparatus is schematically shown in FIG. 1. The system T is formed of an envelope P on the inside of which there is a gel H, in which the drug is dispersed. The system also comprises a microcomputer MC, being fed by a battery B that controls the polarity of two electrodes E and E′. The battery is preferably of the lithium type. When the electrodes are not fed, there is no flow towards the skin of ions corresponding to the drug, whereas when the microcomputer feeds the electrodes, ions F+, corresponding to the drug, are forced to pass through the permeable parts of the envelope towards the skin. At the second electrode there is a passage of sodium ions Na+ from the skin towards a container of saline solution, in order to keep the system neutral. The Fig. refers to the case where the ion corresponding to the drug is positively charged, but the system operates with ions with negative charge F− as well, in this case being balanced by the transportation of chlorine ions Cl− from the skin to the transdermal system. The microcomputer can be programmed for a timed release of the drug. The system can also comprise a push-bottom for releasing the drug upon the patient's request (not shown in the drawing).
The problem that has been observed with active transdermal systems is that the battery releases dimethoxyethane (also indicated in the following as DME), an essential component of the process of manufacturing the batteries, which is kept partly trapped inside thereof. This compound together with water, always present in these systems, forms corrosive solutions attacking the electrical parts, thus leading in time to the loss of functionality of the system. Other acid components can be released by the polymeric material itself forming the envelope. For example, a material commonly employed to make the envelope is Surlyn® (Surlyn® is a registered trademark of the Du Pont company of Wilmington, Del., USA), a mixture of ethylene/(meth)acrylic acid copolymer, other polymers, such as polyesters or nylon, and including charges of metallic salts. It has been observed that in the working conditions of transdermal systems, Surlyn® releases small quantities of acetic acid, which in any case contributes to the problem of corrosion of the electrical parts.
The problem of organic components being released by batteries in general (not necessarily in field of the present application) is known, e.g., from European patent application publication EP 1 115 168 A1. According to the teaching of this document, the problem can be solved by introducing on the inside of the battery a material for the sorption of organic compounds, such as silica, alumina, titanium oxide, or porous solid particles of polymers. The problem of this solution is that, first of all, battery manufacturing is complicated. In addition, in order not to have a continuous removal of organic components of the electrolyte, such as DME or the like (necessary for the battery operation), the sorbing material in this case is coated with a layer of material impermeable to the organic compound, which material dissolves only as a consequence of malfunctions of the battery which cause its overheating. Thereby, this solution is inefficient to absorb the DME quantities, however small, which are released by the battery under normal operating conditions, i.e., when the temperature of the battery does not exceed the foreseen values. Consequently, a battery of the type described in the mentioned patent application would not solve the above-described problems of active systems for transdermal release of drugs.